Argonne National Laboratory (ANL) has developed and is presently demonstrating the electrometallurgical treatment of sodium-bonded metal fuel from Experimental Breeder Reactor II, resulting in an uranium product and two stable waste forms, i.e. ceramic and metallic. Engineering efforts are underway to develop pilot-scale equipment which preconditions irradiated oxide fuel via pyrochemical processing and subsequently allows for electrometallurgical treatment of such non-metallic fuels into standard products and waste forms.
An oxide reduction process preconditions irradiated oxide fuel such that uranium and transuranic (TRU) constituents are chemically reduced into metallic form via a molten Li/LiCI-based reduction system. In this form, the spent fuel is further treated in an electrorefiner and waste handling equipment, thereby reclaiming uranium, and placing TRU elements and fission products into stable forms suitable for disposal in a long-term repository. Development of the Li/LiCI-based oxide reduction process has proceeded at lab scale (nominally 50 grams of heavy metal (HM) and engineering scales (nominally 10-kg of HM) for unirradiated oxide fuel.
The integrated oxide reduction and electrorefining process steps include: 1) preparing the spent fuel for treatment; 2) chemically reducing uranium and TRU constituents; 3) electrorefining the reduced fuel; 4) conditioning the reclaimed uranium and fission product containing waste forms; and 5) regenerating the lithium reductant. Preparation of spent oxide fuel involves chopping fuel elements and loading fuel and cladding into a permeable basket which, heretofore, has been of two different designs, one for the reduction and another for the electrorefining. This invention involves designing a basket which is universal to oxide reduction and electrorefining processes. In the oxide reduction process, lithium and lithium chloride are maintained molten at 650xc2x0 C. When a fuel-loaded basket is placed into this system, the lithium reduces oxides of uranium and TRU constituents into metallic form via the following reaction.
MO2+4Li= greater than 2Li2O+M
(where M=uranium and TRU elements)
The lithium chloride dissolves the resultant lithium oxide from the fuel matrix. Previously, the reduced fuel was physically transferred to a different process container and placed in the electrorefiner, a procedure that is difficult and time consuming. This invention obviates the need for transfer by providing a universal basket design which may be compatible in both the reducing and electrorefining operations.
The new basket containing reduced fuel from the reduction process is placed directly into an electrorefiner, where the uranium is electrochemically dissolved into and transported across a molten lithium/potassium chloride eutectic salt at 500xc2x0 C. Upon completion of the electrorefining process, the uranium product is cast into ingots. The cladding hulls and fission products remaining in the anode basket are processed into a metal waste form. Once fission product or contaminant limits are reached, the TRU and fission product containing salt is processed into a ceramic waste form. An electrowinning process recovers metallic lithium from the salt-soluble lithium oxide and discards the oxygen.
It is an object of the present invention to provide a universal basket useful in both the oxide reduction operation and the electrorefiner part of the anode-cathode module so that material containing uranium values may be transferred from the oxide reduction operation to the electrorefiner by transporting the basket between the two systems.
Another object of the present invention is to provide a basket for use in the reduction of uranium dioxide to uranium metal and in the electrorefining of uranium metal in which the basket includes an inner and outer perforated cylindrical wall defining a continuous annulus therebetween, a screen adjacent to each perforated cylindrical wall, a substantially solid bottom and top plate enclosing the continuous annulus formed by the inner and outer perforated cylindrical walls defining a fuel bed, a plurality of scrapers mounted adjacent to the outer perforated cylindrical wall extending longitudinally thereof, and mechanism enabling the basket to be transported remotely.
Yet another object of the present invention is to provide a universal basket as defined and further including a crucible surrounding the basket, a source of lithium metal substantially surrounding the basket inside the crucible, a source of molten salt containing LiCl substantially saturated with lithium metal in contact with the basket and the source of lithium metal, and impeller mechanism for forcing the molten salt substantially saturated with lithium metal through the inner cylindrical wall in contact with UO2 in the fuel bed to cause UO2 to be reduced to uranium metal.
A final object of the present invention is to provide an anode-cathode module for the electrorefining of uranium, comprising an anode formed by a continuous annular fuel bed defined by inner and outer perforated cylindrical walls having substantially solid top and bottom plates for holding uranium values, a plurality of scrapers circumferentally spaced around the outer perforated cylindrical wall extending longitudinally thereof, a cylindrical cathode spaced from and surrounding the anode defining an annular electrolyte space, the anode and cathode being electrically insulated from each other, and mechanism for causing electrolyte to flow upwardly through the inner perforated cylindrical wall and the annular fuel bed with the uranium values therein rotating said anode with respect to said cathode, the electrolyte flowing into the annular electrolyte space to establish electrotransport of uranium values between the anode and cathode resulting in the precipitation of uranium values on the cylindrical cathode upon establishment of an electrical potential between the anode and cathode.
The invention consists of certain novel features in a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the detail may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.